Fluorescent lamps emit light in all directions; however, in most applications that is not desirable and more than 50% of the light can be wasted. In order to increase the coefficient of light utilization, fixtures employing reflectors are used.
The reflectors are used to recover light that would otherwise be lost (backward lighting), as well as to direct the light where needed (light control).
The reflector design depends upon the application and on lamp geometry and size. The smaller the light source the smaller the reflector and therefore, the smaller the fixture. High output electrodeless lamps (HOEL) are fluorescent lamps that have no electrodes. The discharge in the lamp is generated through a magnetic field coupled through magnetic toroids. The glass vessel of the envelope forms a closed loop and has an overall rectangular shape having two parallel cylindrical glass structures. Such lamps are known and are shown, for example, in U.S. Pat. Nos. 5,834,905 and 6,175,197, the teachings of which are hereby incorporated by reference. The size and shape of these lamps requires relatively large reflectors for two main reason; first, due to the HOEL size and geometry, the reflector must be placed farther away from the lamp to avoid the situation where the reflected light is absorbed by the lamp itself (the farther away from the lamp the larger the reflector needs to be to cover the same solid angle); second is light control. For good light control a light source needs to be a point source. With a point source the direction of the incident light rays is known and the angle of the reflector at each point can be calculated to redirect the light in the proper direction. With a large light source, such as an HOEL, for any given point on the reflector, the incident rays are coming from different directions; therefore, the angle of the reflector at that point can only be a compromise and most of the incident rays will not be redirected in the proper direction. To increase the efficiency and achieve better light control the reflector has to be placed farther away from the lamp; however, this results in a larger fixture.
For economic reasons, as well as aesthetic reasons, a smaller fixture provides many advantages. In many applications, street lighting, for example, the size of the fixture has important cost considerations. As the size of the fixtures increase, so do the weight and the wind resistance, requiring larger mounting posts and larger anchoring with their concomitant cost and labor increases.
The HOEL is an efficient light source; however, due to its size and geometry, large optical systems are required and, therefore, large fixtures. It would be an advance in the art if HOELs could be employed without the disadvantages associated with larger fixtures.